It is known in the art that especially at high vehicle speeds the slip stream strikes the windscreen of the vehicle so forcefully that, during bleed-off, an upward pressure is generated on the wiper blades and on the wiper arms moving across the windscreen, thereby reducing the contact between the windscreen and the wiper blade to such a degree that the cleaning effect of the entire system is markedly decreased. However, in particular, at high speeds perfect cleaning of the windscreen is required in order not to jeopardize the safety of the car passengers.
In the prior art designs according to DE-OS 28 24 014 and DE-PS 40 32 762 the contact force of the wiper arm is variable through a plunger means in that a movable plunger centrally passes through the wiper shaft to swivel an adjusting lever on which is fixed the end of the wiper arm spring facing the shaft in such a way that the line of operation of the spring is varied relative to the axis of the wiper arm, thereby varying the contact force exerted by the wiper arm on the windscreen. However, such arrangements involve the disadvantage that they are complex in design, providing hardly any protection against the ingress of dirt and moisture. Moreover, in view of the adjusting mechanism, the whole system is not sleek which effects not only the outward appearance but also the coefficient of the aerodynamic drag, thereby enhancing the danger of accident.
DE-OS 40 28 494 discloses another adjusting mechanism for windscreen wiper systems of the afore-described type wherein the line of operation of the wiper arm spring is also adjusted relative to the axis of the wiper arm. In that system, the end of the wiper arm spring facing the shaft side is hooked on an adjusting lever, with the latter moving across a sliding insert. The end of the wiper arm spring facing the shaft side is moved toward and away from the windscreen, respectively. A system of this type involves the advantage that it is of a relatively simple design and a low height of construction. However, it has been found to be disadvantageous that when adjusting the line of operation of the wiper arm spring it will be necessary to act against the force of the wiper arm spring involving additional load on the drive of the windscreen wiper system. Moreover, it will be necessary for the swivel bearing of the set lever to take up all of the tension force of the wiper arm spring. As it is especially the adjusting force for the wiper arm spring that is permanently changed, no uniform run (or consistent rate of movement) of the drive of the windscreen wiper system will be possible.
It is, therefore, the object of the invention to improve a windscreen wiper of the afore-mentioned type so as to insure a uniform run and a reduced load on the drive by the forces of the wiper arm spring.
This problem, in the practice of the invention, is solved in that the set element engages a support lever to which is fixed the end of the wiper arm spring facing the shaft side and which, with the end thereof facing away from the wiper shaft, is swivably journalled within a bearing on the mounting portion.
In the arrangement according to the invention, the wiper arm spring, on the one hand, is hooked on the wiper arm and, on the other hand, on the support lever which, in turn, is supported on the mounting portions, so that the whole of the tensile force of the wiper arm spring, in a simple way, is taken up and, through the support lever, is supported on the mounting portion. The adjusting lever of the set element engaging the support lever, hence, no longer is required to take up the tensile force of the wiper are spring, thereby allowing the bearing of the set lever to be designed in an essentially simpler and less rugged way thus enhancing the sensitivity and accuracy of the whole of the adjusting movement. As the support is provided by the support lever, it will also be possible to mount stronger wiper arm springs with no detrimental effect on sensitive bearings of the adjusting mechanism. In the arrangement according to the invention, the contact force is adjusted in that the line of operation of the wiper arm spring relative to the axis of the wiper am is adjusted in that the set lever engages the support lever, swivelling the same about the end thereof facing away from the wiper shaft and fixed, within a bearing, to the mounting portion. As the end of the wiper arm spring facing the shaft side is hooked on the support lever, the said end is also swivelled. The swivel movement is effected with minimal forces as it is not the spring as such but rather the support lever that is swivelled.
The advantage involved herewith resides in that the contact force forcing the wiper blade to the windscreen can be dimensioned to precisely correspond to the position of the wiper blade on the windscreen. Hence, a low contact force can prevail, for example, in the two reversal points of the wiper blade so that the wiping rubber when passing from one wiping position into another is not unnecessarily loaded, thereby also relieving the drive. Moreover, the wiper blade, in its resting position, can be almost completely unloaded thus being exposed to lower deforming forces, thereby enhancing its operating life.
According to an advantageous embodiment of the invention the swivel bearing of the support lever is provided in the vicinity of the hook-on point of the wiper arm spring on the wiper arm so that the forces required for the adjusting movement of the support lever, preferably, can be reduced since in view of the direct vicinity of the swivel bearing of the support lever and the hook-on point of the wiper arm spring only low forces orthogonal to the longitudinal direction of the spring will occur.
An adjustment performed with no force applied can be attained in that the swivel bearing of the support lever on the mounting portion and the hook-on point of the wiper arm spring on the wiper arm coincide. In this way, all of the forces originating from the wiper arm spring are taken up by the support lever. The adjusting movement of the set lever varying the line operation of the wiper arm spring relative to the axis of the wiper arm, will only require bearing and friction forces to be overcome. This giving rise to the advantage that the drive of the windscreen wiper arrangement is not exposed to any additional load.
A high operation safety and minor structural measures for guiding the set lever on the sliding insert are achieved in that the swivel bearing of the support lever relative to the hook-on point of the wiper arm spring on the wiper arm is at a small directional distance so that the set lever of the adjusting mechanism is permanently forced against the sliding insert, thereby insuring that the block of the sliding insert of the set lever safely sweeps across the cam of the sliding insert. In this respect, the force of abutment of the set lever relative to the sliding insert can be so selected that the set lever even in high wiping speeds is not lifted from the sliding insert.
A reduced set force is attained in that the hook-on point of the end of the wiper am spring facing the shaft is fixed at a distance from the end of the support lever facing the shaft side, thereby attaining a favorable lever arm so that the forces between sliding insert and set lever can be further reduced. Due to different support levers with differently arranged hook-on points, the contact force of the wiper blade of the windscreen wiper system, in a simple way, can be varied and adapted in a way specific to the vehicle.
Preferably, the support lever is configured as a dual-leg lever between which the wiper arm spring is arranged. This configuration provides a high degree of safety during the take-up of the spring forces; for increasing the rigidity of the lever it can be of a U-type profile.
The support lever can easily hook on the mounting portion in that the swivel bearing of the support lever is of a fork-type configuration. The support lever is safely held within the bearing through the force of the wiper arm spring.
Advantageously, the wiper arm together with the mounting portion and the sliding insert are designed as an integral unit which involves the advantage that the whole of the arrangement can be easily mounted on the wiper shaft. Moreover, conventional screen wiper arrangements, in a simple way, can be subsequently equipped with the system of the invention.
To protect the adjusting mechanism against the ingress of dirt and moisture, the sliding insert, through an O-ring gasket and/or labyrinth-type pack, is located in the mounting portion through which, advantageously, wear is minimized.
A proper positioning of the sliding insert relative to the position of the mounting portion and of the wiper arm, respectively, is achieved in that the sliding insert is connected to the bearing of the wiper shaft through a feather, a dihedron or the like. This arrangement eliminates the need to subsequently adjust or align the sliding insert after mounting the fixing portion on the shaft; moreover, through the interaction of the sliding insert and the wiper shaft, the precise actuation of the wiper arm spring and the adjustment thereof, respectively, in response to the position of the wiper blade on the screen is safeguarded.
Further advantages, features and details of the invention will become manifest from the following description in which special forms of embodiment are described in detail with reference to the drawings.